FIG. 1-A is a block diagram depicting typical components of a scanner. A scanner is typically used to capture an image of a document 110. A document 110 is placed on the scanner plate 112. A scan head 120, which is generally comprised of an optical subsystem 122 and a charge-coupled device (“CCD”) 124, is moved across the document 110. Although FIG. 1A depicts only a two dimensional view, the scan head 120 may move across the document in both the direction illustrated by arrow 114 and in a direction orthogonal to the document 110. The optical subsystem 122 focuses light reflected from document 110 onto a CCD 124. CCD 124 is often implemented as a two-dimensional array of photosensitive capacitive elements. When light is incident on the photosensitive elements of the CCD 124, charge is trapped in a depletion region of the semiconductor elements. The amount of charge associated with the photosensitive capacitive elements is related to the intensity of light incident on the respective elements received over a sampling period. Accordingly, the image is captured by determining the intensity of incident light at the respective photosensitive capacitive elements via sampling the elements. The analog information produced by the photosensitive capacitive elements is converted to digital information by an analog-to-digital (A/D) converter 130. An A/D converter 130 may convert the analog information received from CCD 124 in either a serial or parallel manner. The converted digital information may be stored in memory 140. The digital information is then processed by a processor 150 according to control software stored in ROM 180. The user may control scanning parameters via user interface 170 and the scanned image is outputted through output port 160.
A block diagram of a digital camera is depicted in FIG. 1B. An optical subsystem 122 of a digital camera may be used to focus light reflected from a document 110 onto a CCD 124, much as in the scanner. In other digital cameras, devices other than a CCD are used to capture the light reflected from the image, such as CMOS sensors. In the context of a digital camera, as opposed to a scanner, the optical subsystem 122 is not moved along the surface of the document, as in a scanner. Rather, in a digital camera, the optical system 122 is generally stationary with respect to the object, such as a document, to be imaged. In addition to digital cameras, photographs captured from film-based cameras may also be digitized.
Cameras offer significant advantages over scanners for capturing document images and other images. For example, cameras are generally more portable than scanners. In addition, because scanners require a captured image to be placed on the scanner plate, cameras are capable of capturing a wider array of images than scanners. However, the use of cameras creates difficulties in image capturing that do not exist when using a scanner. For example, light conditions vary when using a camera, whereas the light conditions are generally controlled in scanners. In addition, use of a camera introduces image distortions, which may depend on various variables, such as the angle of the camera relative to the image, the lens used by the camera and its distance from the image, whether the image including a document is situated on a flat or curved surface and other factors. Because the scanner utilizes a moving scanner head, at a fixed distance from a document to be imaged, these distortions do not generally occur in scanners.
Therefore, a need exists for an apparatus and method for capturing images of documents that utilizes the advantages of cameras over scanners, yet reduces the difficulties presented by capturing document images via a camera as opposed to a scanner.